1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a computer program product.
2. Description of the Related Art
Conventionally widely known are electrophotography image forming apparatuses that transfer and fix a developer, such as a toner, onto a recording medium, such as a recording sheet, thereby performing printing. Such image forming apparatuses can transfer a maximum of 100% of respective color toners onto a recording medium. In the case of using toners of four colors, which are black (K), cyan (C), magenta (M), and yellow (Y), for example, a maximum of 400% of toners are transferred in total onto a recording medium.
However, there is a limit to the total amount of toner that can be fixed to a recording medium. A high-speed cut-sheet color printer used for printing businesses in the production printing field has a limit of approximately 250%, for example.
To address this, Japanese Patent No. 4345295 and Japanese Patent Application Laid-open No. 2001-088371, for example, disclose a technology of total amount control for reducing the amount of toner while preventing a change in colors to be printed as much as possible.
The conventional technologies reduce the total amount of developer by expressing gray, which is usually expressed with developers of CMY, with a developer of K. This results in reduction in the image quality, such as poor reproducibility in a shadow portion and a murky human skin color.
Recently, there have also been developed image processing apparatuses that perform printing with a transparent and colorless developer to make a printed material glossy. Such image processing apparatuses need to transfer a maximum of 100% of the transparent developer to be transferred onto the uppermost portion. To fix all the developers to a recording medium, only a maximum of approximately 150% of the developers of the other colors can be transferred, resulting in a reduced color reproduction range.
Some methods can be employed to perform printing while ensuring a color reproduction range and preventing reduction in the image quality, including a method for performing printing in twice. This method can also perform fixing in twice, making it possible to fix a maximum of approximately 250% of the developers (a maximum of approximately 500% thereof in total) in each fixing.
In a case where the number of colors of the developers used for printing is an odd number, such as 5, printing of a developer of a single color possibly needs to be performed in twice. In this case, dithering of the single color needs to be performed in twice.
Therefore, there is a need for an image processing apparatus, an image processing method, and a computer program product that are capable of performing dithering of a single color in twice.